Concept:Surah At-Takathur warns against excessive worldly competition and materialism.Explanation:The core lesson of Surah At-Takathur is that engrossment in accumulating wealth and boasting about possessions diverts people from the remembrance of Allah.This preoccupation continues until death, which should remind believers of the Hereafter and accountability.The surah emphasizes that piling up wealth and striving for more worldly gains leads to negligence of spiritual duties.Therefore, a Muslim should avoid the obsession with increasing and hoarding wealth.Answer:C. piling of wealth